Submicron Spatial Resolution Research Articles

Bond-selective transient phase imaging via sensing of the infrared photothermal effect

Phase-contrast microscopy converts the phase shift of light passing through a transparent specimen, e.g., a biological cell, into brightness variations in an image. This ability to observe structures without destructive fixation or staining has been widely utilized for applications in materials and life sciences. Despite these advantages, phase-contrast microscopy lacks the ability to reveal molecular information. To address this gap, we developed a bond-selective transient phase (BSTP) imaging technique that excites molecular vibrations by infrared light, resulting in a transient change in phase shift that can be detected by a diffraction phase microscope. By developing a time-gated pump–probe camera system, we demonstrate BSTP imaging of live cells at a 50 Hz frame rate with high spectral fidelity, sub-microsecond temporal resolution, and sub-micron spatial resolution. Our approach paves a new way for spectroscopic imaging investigation in biology and materials science.

CBMT-07. BIOMARKERS OF AGGRESSIVENESS IN IDH MUTANT GLIOMA

Abstract BACKGROUND Gliomas with isocitrate dehydrogenase (IDH) mutations in adults evolve from lower-grade gliomas to secondary glioblastomas (GBM), a fatal disease with fast progression. IDH mutation occurs early in tumorigenesis, and persistently contribute to the reprograming of glucose, lipid and amino acid metabolism. This offer a plethora of potential biomarkers of progression. However, because it is extremely difficult to detect the distribution and transfer of metabolites changing in every moment in a single cell, the involvement of metabolites produced by mutant IDH in malignant progression remains understudied. MATERIALS AND METHODS Raman imaging spectroscopy, which can image chemical bonds and concentration of molecules at submicron spatial resolution, enables detection of spatiotemporal changes of metabolomes in live cells. We developed the software called Biomolecular Component Analysis (BCAbox) to deconvolute the recorded raw Raman spectra, leading to detection of unique spectral features of different classes of biomolecules. RESULTS AND CONCLUSIONS We applied Raman imaging spectroscopy to GBM cell lines that were transfected with IDH1 mutant gene. Our results indicated that lipid metabolism has a unique profile in IDH1 mutant gliomas. Subsequent mass spectrometry analysis of extracted organelle revealed the exact classes of lipids altered in the IDH mutant glioma and suggested biomarkers unique to IDH1 mutant. We will report our validation studies of the biomarkers in patient-derived IDH mutant glioma cell lines and patients derived-orthotopic xenograft mouse models with different degrees of aggressiveness and in matched primary versus recurrent gliomas. The results of the present study may provide novel insights into the discovery of metabolic biomarkers for the malignant progression in IDH mutant gliomas.

Design for a high resolution electron energy loss microscope

An electron optical column has been designed for High Resolution Electron Energy Loss Microscopy (HREELM). The column is composed of electron lenses and a beam separator that are placed between an electron source based on a laser excited cesium atom beam and a time-of-flight (ToF) spectrometer or a hemispherical analyzer (HSA). The instrument will be able to perform full field low energy electron imaging of surfaces with sub-micron spatial resolution and meV energy resolution necessary for the analysis of local vibrational spectra. Thus, non-contact, real space mapping of microscopic variations in vibrational levels will be made possible. A second imaging mode will allow for the mapping of the phonon dispersion relations from microscopic regions defined by an appropriate field aperture.

Radionuclide-bearing minerals in Olympic Dam copper concentrates

Olympic Dam hosts >80 million tonnes of copper, as copper‑iron sulphides, within hematite-dominant gangue. Processing of the relatively fine-grained copper ore is complicated by the presence of by-product uranium and its radiogenic isotopes, in particular 226Ra, 210Pb and 210Po, which partially recover to the final copper sulphide concentrates. Although the majority (~85%) of the U-bearing minerals (uraninite, coffinite, brannerite, thorianite, thorite) are recovered to flotation tailings, the remaining ~15% occurs in copper concentrates as sulphide-gangue composite particles and micron- to nanoscale grains occluded within sulphide minerals. Sulphuric acid leaching of copper concentrates significantly reduces the concentration of U but has only a minor impact on the daughter isotopes. Further reduction of these isotopes may be achieved through selective targeting and removal of specific minerals known to be radionuclide (RN) hosts, but fine-grained, micro- to nanoscale ore textures preclude easy direct identification of these RN host phases.Nanoscale secondary ion mass spectrometry (nanoSIMS) has proven to be an excellent platform for in situ mapping of ultra-trace RN distributions, with sub-micron spatial resolution, in individual mineral grains. Uranium and thorium minerals are, as expected, the major hosts and display significant concentrations of the entire 238U decay chain. Although the majority of these minerals are removed via acid leaching of copper concentrate, sufficient RNs remain in the concentrate as micron- to nanoscale grains within sulphides and gangue minerals or along particle microfractures. Results show that brannerite, potentially more problematic due to its lower solubility in sulphuric acid than uraninite, does not appear to contain appreciable amounts of daughter isotopes. The insolubility of ThPO4 produces the potential for sequestration of 232Th and 230Th in rare earth phosphates such as xenotime, which then retain the respective decay chains. Likewise, the insolubility of certain sulphates (Sr, Ba, Pb, Ra) provides a mechanism for precipitation and entrapment of RNs. Baryte was shown to accumulate Ra and Pb naturally in the deposit, and it can upgrade its RN content substantially during sulphuric acid leaching through coupled dissolution-reprecipitation mechanisms involving Pb2+ and Ra2+ liberated from dissolved uranium minerals. Identification and prioritization of RN host minerals is crucial for the development of a more efficient processing flowsheet.

Microbeam synchrotron radiation diffraction and fluorescence of oxide layers formed on zirconium alloys at different corrosion temperatures

Autoclave corrosion tests of Zircaloy-4 were performed at temperatures ranging from 274°C to 427 °C to determine how the characteristics of the oxide layer changed with corrosion temperature. Corroded samples were prepared in cross-section and examined at the Advanced Photon Source using x-ray diffraction and fluorescence with sub-micron spatial resolution. These measurements provide high fidelity data for characterization of the oxide layer grown on zirconium alloys over a range of temperatures to better understand the fundamental mechanisms of corrosion. It was found that the size of the monoclinic oxide grains increases with distance from the metal-oxide interface, while the average grain size of the tetragonal oxide phase decreases. This is consistent with the continuous nucleation of a mixture of equiaxed tetragonal and monoclinic grains at the metal-oxide interface, of which only the monoclinic oxide grains that are properly aligned to minimize stresses grow into long columnar oxide grains. The tetragonal phase oxide grains transform to monoclinic oxide once a critical size is reached. While the monoclinic oxide grain size increases with corrosion temperature, the tetragonal phase grain size remains below a maximum value. Evolution of the tetragonal fraction, calculated with the Garvie-Nicholson formula, was observed, with local maxima seen just before transition and local minima seen at oxide locations corresponding to the oxide kinetic transition. No difference was observed in the tetragonal phase fraction in the oxide layers formed at different corrosion temperatures. Detailed fluorescence and diffraction mapping of one sample showed the evolution of the diffraction intensity over a short range in the oxide. This work provides a systematic study revealing fundamental characteristics of the microstructure of Zircaloy-4 oxide layers to further understanding of corrosion resistance of these materials.

Revealing the Elemental Distribution within Latent Fingermarks Using Synchrotron Sourced X-ray Fluorescence Microscopy.

Fingermarks are an important form of crime-scene trace evidence; however, their usefulness may be hampered by a variation in response or a lack of robustness in detection methods. Understanding the chemical composition and distribution within fingermarks may help explain variation in latent fingermark detection with existing methods and identify new strategies to increase detection capabilities. The majority of research in the literature describes investigation of organic components of fingermark residue, leaving the elemental distribution less well understood. The relative scarcity of information regarding the elemental distribution within fingermarks is in part due to previous unavailability of direct, micron resolution elemental mapping techniques. This capability is now provided at third generation synchrotron light sources, where X-ray fluorescence microscopy (XFM) provides micron or submicron spatial resolution and direct detection with sub-μM detection limits. XFM has been applied in this study to reveal the distribution of inorganic components within fingermark residue, including endogenous trace metals (Fe, Cu, Zn), diffusible ions (Cl-, K+, Ca2+), and exogeneous metals (Ni, Ti, Bi). This study incorporated a multimodal approach using XFM and infrared microspectroscopy analyses to demonstrate colocalization of endogenous metals within the hydrophilic organic components of fingermark residue. Additional experiments were then undertaken to investigate how sources of exogenous metals (e.g., coins and cosmetics) may be transferred to, and distributed within, latent fingermarks. Lastly, this study reports a preliminary assessment of how environmental factors such as exposure to aqueous environments may affect elemental distribution within fingermarks. Taken together, the results of this study advance our current understanding of fingermark composition and its spatial distribution of chemical components and may help explain detection variation observed during detection of fingermarks using standard forensic protocols.

Cross-sectional hyperspectral imaging of proton implanted diamond

Cross-sectional Raman/photoluminescence hyperspectral imaging was employed to study the formation and annealing behavior of optical centers in diamond, which was implanted by a focused 2 MeV proton beam. The resulting compact implantation profiles, together with the submicron spatial resolution of the hyperspectral imaging technique, produced detailed distributions of the nitrogen-vacancy centers and the TR12 center. In addition, cluster analysis was used to identify a split in the implantation end of range into two subregions, each with its own characteristic emission spectrum centered at 543 nm and 552 nm. We demonstrate that our analysis methodology on the hyperspectral dataset, paired with the use of focused beam implantation, provides a renewed understanding of defect formation and lattice damage in ion-implanted single crystal diamond.

Non-destructive optical second harmonic generation imaging of 3D printed aluminum nitride ceramics

Abstract Aluminum nitride (AlN) ceramics have attracted broad interest due to their potential applications in electronics. Additive manufacturing of ceramic components are rapidly advancing, could provide a new way of manufacturing over conventional methods. Non-destructive testing of 3D printed ceramic samples is an important step for quality control in manufacturing. Here we show that AlN ceramics show strong optical second harmonic generation (SHG) signals due to its wurtzite crystal structure. Microscopic SHG imaging can also examine the microscopy domains in AlN ceramics with submicron spatial resolution. This technique has the potential to be applied as a non-destructive testing method for examining 3D printed AlN ceramic components.

Longitudinal strain of epitaxial graphene monolayers on SiC substrates evaluated by z-polarization Raman microscopy

Longitudinal strains in epitaxial monolayer graphene (EMG) grown on SiC substrates were evaluated by z-polarization Raman microscopy. Due to the covalent bonds formed at the interface between graphene and the substrate, strong compressive strains were loaded on the EMG, which were sensitively detected by Raman spectroscopy. Our polarization Raman microscope was specially designed for evaluating the longitudinal (z-polarization) strain, as well as the lateral (xy-polarization). Z-polarization Raman microscopy revealed the relationship between the fluctuation of the local strains and the sample morphology in the SiC-graphene through submicron spatial resolution mapping. The amount of strain estimated through Raman shift and its spatial inhomogeneity have critical influence on the mobility of electrons, which are essential for future device applications of EMG.

Detection of Trace Elements/Isotopes in Olympic Dam Copper Concentrates by nanoSIMS

Many analytical techniques for trace element analysis are available to the geochemist and geometallurgist to understand and, ideally, quantify the distribution of trace and minor components in a mineral deposit. Bulk trace element data are useful, but do not provide information regarding specific host minerals—or lack thereof, in cases of surface adherence or fracture fill—for each element. The CAMECA nanoscale secondary ion mass spectrometer (nanoSIMS) 50 and 50L instruments feature ultra-low minimum detection limits (to parts-per-billion) and sub-micron spatial resolution, a combination not found in any other analytical platform. Using ore and copper concentrate samples from the Olympic Dam mining-processing operation, South Australia, we demonstrate the application of nanoSIMS to understand the mineralogical distribution of potential by-product and detrimental elements. Results show previously undetected mineral host assemblages and elemental associations, providing geochemists with insight into mineral formation and elemental remobilization—and metallurgists with critical information necessary for optimizing ore processing techniques. Gold and Te may be seen associated with brannerite, and Ag prefers chalcocite over bornite. Rare earth elements may be found in trace quantities in fluorapatite and fluorite, which may report to final concentrates as entrained liberated or gangue-sulfide composite particles. Selenium, As, and Te reside in sulfides, commonly in association with Pb, Bi, Ag, and Au. Radionuclide daughters of the 238U decay chain may be located using nanoSIMS, providing critical information on these trace components that is unavailable using other microanalytical techniques. These radionuclides are observed in many minerals but seem particularly enriched in uranium minerals, some phosphates and sulfates, and within high surface area minerals. The nanoSIMS has proven a valuable tool in determining the spatial distribution of trace elements and isotopes in fine-grained copper ore, providing researchers with crucial evidence needed to answer questions of ore formation, ore alteration, and ore processing.

A Scanning Optical Quantum Magnetometer Based on the Hole Burning Phenomenon

A scanning optical quantum magnetometer with submicron spatial resolution is proposed that is based on the phenomenon of hole burning in the signal of optically detected magnetic resonance (ODMR) on atomic-sized color centers in silicon carbide crystals under conditions of spin level saturation by means of additional high-frequency resonance pumping. An increase in the sensitivity is achieved due to narrowing of the ODMR line and increasing slope of the dependence of signal frequency on the magnetic field.

High Temperature Oxidation of Zircaloy-4 Under Conditions Simulating a Loss of Cooling Accident in Spent Fuel Pools Examined with Raman Imaging and 18O Tracer Techniques

Since the Fukushima accident, an increased attention is continuously paid to the vulnerability of the Spent Fuel Pools (SFPs). In SFPs, for different reasons, degradation of the fuel rods induced by oxidation in air-steam mixtures after dewatering is a major safety concern: (i) the cladding material is the only barrier left against fission product dissemination, (ii) the heat released by the oxidation reactions can overcome the residual decay heat of the fuel and may become the main driving force to the accident escalation, (iii) hydrogen production is a strong concern because of the presence of steam, (iv) presence of air in the atmosphere is known to be an aggravating factor because of the “catalytic” role of nitrogen on the oxidation mechanism. In this study, high temperature oxidation tests in oxygen, air and air - steam atmospheres were performed with Zircaloy-4 cladding tubes and plates specimens. Because spent fuels are concerned, the presence of the corrosion oxide scale formed in reactor during in-service operation was also considered. The tests described in this study were restricted to the 700 – 950°C range, and mostly performed at 850°C. Raman imaging was used to examine the specimens after the oxidation tests, either directly at the oxide surface, or on metallographic preparations for cross-section examinations. We first used new opportunities given by Raman imaging to analyze, at least qualitatively, the structural and mechanical phenomena involved in this particular corrosion phenomena. Indeed, this method can provide information on the nature of phases that are present in the scale and on the stress level with sub-micron spatial resolution. The different methods used to extract this information that is present in the Raman data will be described and discussed. Moreover, isotopic substitution was also considered. Actually, Raman spectroscopy has also the ability to quantitatively extract the 18O distribution in a zirconia oxide scale after a two stage experiment with a fair accuracy. Raman imaging gave clear evidence for different characteristic distributions of 18O in the scales. Some of them have been correlated with the development of cracks and porosity in the oxide which allows the corroding medium to penetrate locally in the scales. Nitrogen appears to have no or limited influence on the oxygen diffusion, but is observed to reach the metal/oxide interface much faster than oxygen. Thus, we also emphasize the potential of this method to investigate the 18O distribution in such complex corrosion scales.

Application of nuclear emulsions for the identification of multi-MeV protons in laser ion acceleration experiments

Nuclear emulsions are applied to identify multi-MeV protons accelerated by an intense PW-class laser. Although nuclear emulsions, which record the three-dimensional trajectories of charged particles, feature high sensitivity and a sub-micron spatial resolution, they have never been used for the detection of laser-accelerated ions. This is because intense laser-matter interactions generate not only ions but also copious electrons, including secondary electrons induced by X-rays, which are recorded as background noise in a nuclear emulsion. Therefore, it is not a trivial task to identify ion tracks in a nuclear emulsion exposed to such extreme mixed radiation fields. Here, for the first time, we have succeeded in identifying the signals from laser-accelerated protons in nuclear emulsions by suppressing the background noise signals through the use of desensitized development conditions, i.e., a developer solution with a pH of 7.3 and a development time of 25 min. The energy spectrum obtained from a stack of nuclear emulsion films shows good agreement with that obtained from a stack of films of the conventional solid-state nuclear track detector material CR-39, which is sensitive only to ions. An additional benchmark experiment with 100-MeV protons from a conventional accelerator apparatus confirms that nuclear emulsions have the potential to measure 100-MeV-class laser-accelerated protons.

Oxygen-Induced In Situ Manipulation of the Interlayer Coupling and Exciton Recombination in Bi2Se3/MoS2 2D Heterostructures.

Two-dimensional (2D) heterostructures are more than a sum of the parent 2D materials, but are also a product of the interlayer coupling, which can induce new properties. In this paper, we present a method to tune the interlayer coupling in Bi2Se3/MoS2 2D heterostructures by regulating the oxygen presence in the atmosphere, while applying laser or thermal energy. Our data suggest that the interlayer coupling is tuned through the diffusive intercalation and deintercalation of oxygen molecules. When one layer of Bi2Se3 is grown on monolayer MoS2, an influential interlayer coupling is formed, which quenches the signature photoluminescence (PL) peaks. However, thermally treating in the presence of oxygen disrupts the interlayer coupling, facilitating the emergence of the MoS2 PL peak. Our density functional theory calculations predict that intercalated oxygen increases the interlayer separation ∼17%, disrupting the interlayer coupling and inducing the layers to behave more electronically independent. The interlayer coupling can then be restored by thermally treating in N2 or Ar, where the peaks will requench. Hence, this is an interesting oxygen-induced switching between "non-radiative" and "radiative" exciton recombination. This switching can also be accomplished locally, controllably, and reversibly using a low-power focused laser, while changing the environment from pure N2 to air. This allows for the interlayer coupling to be precisely manipulated with submicron spatial resolution, facilitating site-programmable 2D light-emitting pixels whose emission intensity could be precisely varied by a factor exceeding 200×. Our results show that these atomically thin 2D heterostructures may be excellent candidates for oxygen sensing.

Sub-Micron Spatial Resolution in Far-Field Raman Imaging Using Positivity-Constrained Super-Resolution.

Raman microscopy is a valuable tool for detecting physical and chemical properties of a sample material. When probing nanomaterials or nanocomposites the spatial resolution of Raman microscopy is not always adequate as it is limited by the optical diffraction limit. Numerical post-processing with super-resolution algorithms provides a means to enhance resolution and can be straightforwardly applied. The aim of this work is to present interior point least squares (IPLS) as a powerful tool for super-resolution in Raman imaging through constrained optimization. IPLS's potential for super-resolution is illustrated on numerically generated test images. Its resolving power is demonstrated on Raman spectroscopic data of a polymer nanowire sample. Comparison to atomic force microscopy data of the same sample substantiates that the presented method is a promising technique for analyzing nanomaterial samples.

Visualizing the Effect of an Electrostatic Gate with Angle-Resolved Photoemission Spectroscopy.

Electrostatic gating is pervasive in materials science, yet its effects on the electronic band structure of materials has never been revealed directly by angle-resolved photoemission spectroscopy (ARPES), the technique of choice to noninvasively probe the electronic band structure of a material. By means of a state-of-the-art ARPES setup with submicron spatial resolution, we have investigated a heterostructure composed of Bernal-stacked bilayer graphene (BLG) on hexagonal boron nitride and deposited on a graphite flake. By voltage biasing the latter, the electric field effect is directly visualized on the valence band as well as on the carbon 1s core level of BLG. The band gap opening of BLG submitted to a transverse electric field is discussed and the importance of intra layer screening is put forward. Our results pave the way for new studies that will use momentum-resolved electronic structure information to gain insight on the physics of materials submitted to the electric field effect.

Identification of point defects using high-resolution electron energy loss spectroscopy

Although there are many techniques that can detect bandgap states associated with point defects in the lattice, it is not routinely possible to determine the type of defect at submicron spatial resolution. Here we show that high-resolution electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope can locate and identify point defects with a resolution of about 10 nm in a wide-bandgap BAlN semiconductor. B interstitials, N vacancies, as well as other point defects have been experimentally detected using EELS and have been identified using density functional theory.

Polarization dependence of angle-resolved photoemission with submicron spatial resolution reveals emerging one-dimensionality of electrons in NbSe3

The work at Lausanne and Geneva is supported by the Swiss NSF. M.A.V. acknowledges financial support from Spanish MICIN Postdoctoral Mobility Program. S.P. acknowledges C’NANO Ile-de-France, DIM NanoK, for the support of the Nanospecs project. Work in Spain was supported by a MINECO (Grants FIS2015-64886-C5-4-P and CTQ2015-64579-C3-3-P), Generalitat de Catalunya (2017SGR1506 and 2017SGR1289), and XRQTC. E.C. acknowledges support from MINECO through the Severo Ochoa Centers of Excellence Program under Grant No. SEV-2015-0496. ICN2 is funded by the CERCA Program/ Generalitat de Catalunya, and supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV- 2017-0706). P.A. acknowledges support from the Maria de Maeztu Units of Excellence Program under Grant MDM- 2017-0767. S.C. gratefully acknowledges the Becas Chile program (CONICYT PAI/INDUSTRIA 72090772) for a doctoral grant at the Universitat de Barcelona. Synchrotron SOLEIL is supported by the Centre National de la Recherche Scientifique (CNRS) and the Commissariat a l’Energie Atomique et aux energies Alternatives (CEA).

Conceptual Design for a Microfocus Beamline on the SKIF Synchrotron

A design is proposed for a fourth-generation synchrotron beamline for investigating the structure and composition of a broad range of samples with high (submicron) spatial resolution.

Modular soft robotic microdevices for dexterous biomanipulation.

We present a methodology for building biologically inspired, soft microelectromechanical systems (MEMS) devices. Our strategy combines several advanced techniques including programmable colloidal self-assembly, light-harvesting with plasmonic nanotransducers, and in situ polymerization of compliant hydrogel mechanisms. We synthesize optomechanical microactuators using a template-assisted microfluidic approach in which gold nanorods coated with thermoresponsive poly(N-isopropylmethacrylamide) (pNIPMAM) polymer function as nanoscale building blocks. The resulting microactuators exhibit mechanical properties (4.8 ± 2.1 kPa stiffness) and performance metrics (relative stroke up to 0.3 and stress up to 10 kPa) that are comparable to that of bioengineered muscular constructs. Near-infrared (NIR) laser illumination provides effective spatiotemporal control over actuation (sub-micron spatial resolution at millisecond temporal resolution). Spatially modulated hydrogel photolithography guided by an experimentally validated finite element-based design methodology allows construction of compliant poly(ethylene glycol) diacrylate (PEGDA) mechanisms around the microactuators. We demonstrate the versatility of our approach by manufacturing a diverse array of microdevices including lever arms, continuum microrobots, and dexterous microgrippers. We present a microscale compression device that is developed for mechanical testing of three-dimensional biological samples such as spheroids under physiological conditions.